1. Field of the Invention
The present invention relates to an apparatus for continuous polymerization of olefin(s) including a plurality of serially-disposed gas-phase polymerization reactors, in which a gas accompanying a polymer powder produced in an upstream reactor is exchanged with another gas and then the polymer powder can be transferred intermittently or continuously to a downstream reactor. The present invention relates also to a method for transferring a polymer powder and a method for continuous polymerization of olefin(s) using the apparatus.
2. Description of the Related Art
In a fluidized-bed reactor for gas-phase polymerization of olefin(s), a fluidized bed has been formed in which a polymer powder flows by virtue of a reaction gas stream. When the polymer powder is drawn off from the reactor, it necessarily is accompanied by the reaction gas which has coexisted with the polymer powder. The reaction gas, which is composed mainly of feedstock olefin gas, may additionally contain a sub-raw material gas needed for causing a desired polymerization reaction in a reactor. In some cases, the sub-raw material gas may be obstructive to the following steps. For example, when hydrogen, which serves as a molecular weight regulator, is used as a sub-raw material gas in a multi-stage polymerization apparatus including a plurality of reactors and if hydrogen in an amount more than that required for a reaction in the following step is contained in the accompanying gas, it will become difficult to produce a polymer with a desired molecular weight and, accordingly, the range of the composition of polymers obtainable may be limited. For solving such problems, methods for separating, as much as possible, a sub-raw material gas accompanying a polymer powder drawn off from a reactor have been proposed.
For instance, U.S. Pat. No. 4,621,952 discloses a method in which two polymer settling vessel are disposed in parallel after a gas-phase polymerization reactor and a polymer powder is transferred to the following step alternately and a method using two polymer settling vessels are disposed serially after a gas-phase polymerization reactor wherein a polymer is separated in a first vessel and transferred to a second vessel and then the polymer separated is transferred to the following step. For improving the polymer separation efficiency in the first vessel in the case of using the serially-disposed two vessels, JP-A 2000-53707 discloses an approach of causing the first vessel to have a conduit with a large opening for receiving the polymer. JP-A 3-153708 discloses a method in which a settling vessel is provided with a pressure leveling line and a polymer powder settled is discharged together with a small amount of gas intermittently to the following step. U.S. Pat. No. 5,928,612 discloses a method in which a drawing-off conduit from a gas-phase polymerization vessel is directed downwards in a predetermined angle. However, these approaches require two polymer settling vessels, resulting in difficulty in continuous operations or difficulty in changing the gas exchange rate at will.